Honeycomb structural body

ABSTRACT

An object of the present invention is to provide a honeycomb structural body for use in a filter, which can support a large amount of catalysts, can suppress increase in pressure loss upon collecting particulates, can have a high particulate collecting capability and can efficiently carry out a regenerating process and a toxic gas purifying process. The honeycomb structural body according to the present invention is a pillar-shaped honeycomb structural body having a structure in which a plurality of through holes are placed in parallel with one another in the length direction with a partition wall interposed therebetween, wherein lamination members are laminated in the length direction so that the through holes are superposed on one another, and one of ends of each through hole is sealed.

TECHNICAL FIELD

This application claims benefit of priority to Japanese PatentApplication No. 2003-197385, filed on Jul. 15, 2003, and Japanese PatentApplication No. 2003-376227, filed on Nov. 5, 2003, the contents ofwhich are incorporated by reference herein.

The present invention relates to a honeycomb structural body that isused in order to remove particulates, etc. contained in exhaust gasesdischarged from an internal combustion engine such as a diesel engine.

BACKGROUND ART

Recently, particulates, such as soot, contained in exhaust gases thatare discharged from internal combustion engines of vehicles, such asbuses and trucks, and construction machines, have raised seriousproblems as those particulates are harmful to the environment and thehuman body. Conventionally, various filters, which are used forcollecting particulates in exhaust gases so as to purify the exhaustgases, have been proposed, and filters having a honeycomb structure havealso been proposed.

FIG. 4 is a perspective view that shows one type of filter having such ahoneycomb structure.

This honeycomb filter 60, which is prepared as a honeycomb structuralbody made from silicon carbide and the like, has a structure in which aplurality of square-pillar shaped porous ceramic members 70 are combinedwith one another through sealing material layer 64 that serve as abonding agent to form a ceramic block 65, and a sealing material layer63 is also formed on the circumference of this ceramic block 65.

FIG. 5(a) is a perspective view that schematically shows the porousceramic member constituting the honeycomb filter shown in FIG. 4, andFIG. 5(b) is a cross-sectional view taken along line B-B of the porousceramic member shown in FIG. 5(a).

The porous ceramic member 70 has a honeycomb structure in which apartition wall 73, which separates a large number of through holes 71that are placed in parallel with one another in the length direction,serves as a filter.

In other words, as shown in FIG. 5(b), each of the through holes 71,formed in the porous ceramic member 70, is sealed with a plug 72 ateither of ends of its exhaust gas inlet side or outlet side so thatexhaust gases that have entered one through hole 71 are discharged fromanother through hole 71 after having always passed through eachpartition wall 73 that separates the through holes 71.

Here, the sealing material layer 63 formed on the circumference isplaced in order to prevent exhaust gases from leaking from theperipheral portion of the ceramic block 65, when the honeycomb filter 60is installed in an exhaust passage of an internal combustion engine.

When the honeycomb filter 60 having such a structure is placed in theexhaust passage of an internal combustion engine, particulates inexhaust gases discharged from the internal combustion engine arecaptured by the partition wall 73 upon passing through the honeycombfilter 60 so that the exhaust gases are purified.

A filter having such a honeycomb structure, which can collectparticulates in exhaust gases, is also designed so that a catalyst usedfor purifying exhaust gases is adhered to a portion (through holes andthe like) functioning as a filter; thus, the filter makes it possible topurify toxic components such as CO, HC and NOx in exhaust gases, toaccelerate activation of oxygen, NOx, etc. by the catalyst, and also toreduce activation energy for burning particulates adhered to thecatalyst so that the particulates can be burned at low temperatures.

Conventionally, with respect to the filter having the honeycombstructure to which the catalyst is attached, a porous ceramic honeycombstructure formed by refractory particles made from silicon carbide,cordierite or the like has been widely used, and a structural body inwhich a plurality of porous ceramic members are combined with oneanother in the length direction through a bonding agent, a structuralbody which is formed through an extrusion molding process into anintegral structure made from ceramics and the like have been generallyused (for example, see Patent Document 1).

With respect to the above-mentioned filter using a catalyst, it ispreferable to increase reaction sites between the particulates and thecatalyst. In order to achieve this structure, it is effective toincrease the porosity in a wall portion constituting the honeycombstructural body so that a large number of open pores are includedtherein; thus, more particulates are collected also in the inner side ofthe wall portion (hereinafter, referred to as deep-layer filtration) sothat the particulates are also made in contact with the catalyst adheredto the inner side of the wall portion.

However, when the above-mentioned methods are used in the porous ceramichoneycomb structural body made from refractory particles, the strengthof the filer becomes very low. For this reason, upon burning andremoving collected particulates (hereinafter, referred to as aregenerating process) in such a filter, the filter tends to generate agreat temperature difference in the length direction of the filter dueto the burning process of the particulates, resulting in damages such ascracks in the filter due to the resulting thermal stress. Consequently,the above-mentioned filter tends to lose functions as the filter.

Moreover, with respect to the filter having a honeycomb structure towhich a catalyst is applied, a honeycomb structural body manufactured byextrusion-molding a mixture containing inorganic fibers such as aluminaand silica, and a honeycomb structural body which is manufactured bycorrugating inorganic sheets, which is obtained from inorganic fibersthrough a paper-making process, have been known (for example, see PatentDocuments 2 and 3).

In addition to these, with respect to the filter having a honeycombstructure to which a catalyst is applied, a honeycomb structural bodyusing a metal porous material has also been known (for example, seePatent Documents 4 to 6).

Although the honeycomb structural body using the metal porous materialis capable of maintaining sufficient strength even when the porosity isincreased, the filtering area becomes very small because of itsstructure to cause a high flowing rate in exhaust gases upon passingthrough the filter wall portion and the subsequent high pressure loss inthe filter.

Here, with respect to the filter having a honeycomb structure to which acatalyst is applied, a honeycomb structural body in which a plurality ofhoneycomb ceramic modules, each having a predetermined thickness, areplaced with open-hole cells communicating with each other has also beenproposed (for example, see Patent Document 7).

Such a honeycomb structural body formed by placing a plurality of thehoneycomb ceramic modules makes it possible to alleviate a thermalstress caused by a temperature difference in the filter lengthdirection.

Regarding the honeycomb ceramic modules which forms a honeycombstructural body by placing a plurality of those, the honeycomb ceramicmodules formed by extrusion-molding a mixture containing refractoryparticles and inorganic fibers made from alumina, silica and the like,into a honeycomb structure and then firing the resulting formed body;and the honeycomb ceramic modules formed by perforating inorganicsheets, which are prepared by subjecting inorganic fibers to papermakingprocess, to form a honeycomb shape have been known.

However, the honeycomb filter constituted by the former honeycombceramic modules has no plugged portions, resulting in degradation in theparticulate collecting efficiency.

Moreover, the filter having a honeycomb structure is normally used athigh temperatures while it is put into a casing (metal container);however, in the case where the former honeycomb structural body formedby placing a plurality of honeycomb ceramic modules is directly put intothe casing, since its coefficient of thermal expansion is greatlydifferent from that of the casing (metal container), gaps occur betweenthe modules and the casing (metal container) located on thecircumference thereof as well as between the honeycomb ceramic modules;thus, exhaust gases flow out through the gaps, resulting in a leak ofcollected particulates and the subsequent reduction in the particulatecollecting efficiency.

-   -   Patent Document 1: JP-A 06-182228 (1994)    -   Patent Document 2: JP-A 04-2674 (1992)    -   Patent Document 3: JP-A 2001-252529    -   Patent Document 4: JP-A 06-257422 (1994)    -   Patent Document 5: JP-A 06-294313 (1994)    -   Patent Document 6: JP-A 09-49420 (1997)    -   Patent Document 7: JP-A 08-12460 (1996)

DISCLOSURE OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

The present invention has been devised so as to solve theabove-mentioned problems, and its objective is to provide a honeycombstructural body which has a high collecting efficiency of particulates,and is less likely to be damaged even when a porosity is increased, andcan be used for a long time. Moreover, another objective of the presentinvention is to provide a honeycomb structural body which can reduce apressure loss after particulates have been collected. The otherobjective of the present invention is to provide a honeycomb structuralbody which can be adjusted into a complex shape.

MEANS FOR SOLVING THE PROBLEMS

A honeycomb structural body in accordance with a first aspect of thepresent invention is a pillar-shaped honeycomb structural body having astructure in which a plurality of through holes are placed in parallelwith one another in the length direction with a partition wallinterposed therebetween, wherein lamination members are laminated in thelength direction so that the through holes are superposed on oneanother, and one of ends of each through hole is sealed.

A honeycomb structural body in accordance with a second aspect of thepresent invention is a pillar-shaped honeycomb structural body having astructure in which a plurality of through holes are placed in parallelwith one another in the length direction with a partition wallinterposed therebetween, wherein lamination members are laminated in thelength direction so that the through holes are superposed on oneanother, and at least the lamination members positioned on both endfaces of the honeycomb structural body are mainly made of metal.

In the honeycomb structural body of the second aspect of the presentinvention, preferably, all the lamination members are mainly made ofmetal. Moreover, in the honeycomb structural body of the second aspectof the present invention, preferably, each of a plurality of the throughholes is sealed at one of the ends of the honeycomb structural body, andthe honeycomb structural body functions as a filter.

In the honeycomb structural bodies of the first and second aspects ofthe present invention, preferably, a catalyst is supported on thelamination members.

The honeycomb structural bodies of the first and second aspects of thepresent invention preferably function as exhaust gas purifying filters.

The honeycomb structural bodies of the first and second aspects of thepresent invention are in common with each other in that each of them hasa pillar-shaped honeycomb structural body in which a plurality ofthrough holes are placed in parallel with one another in the lengthdirection with a partition wall interposed therebetween, and in thatlamination members are laminated in the length direction so that thethrough holes are superposed on one another; however, the honeycombstructural body of the first aspect of the present invention has astructure in which one of the ends of each through hole is sealed, whilethe honeycomb structural body of the second aspect of the presentinvention does not necessarily have the structure in which one of theends of each through hole is sealed, which makes the two honeycombstructural bodies different from each other. Also, the honeycombstructural body of the second aspect of the present invention has astructure in which at least the lamination members positioned on bothend faces of the honeycomb structural body are mainly made of metal,while the honeycomb structural body of the first aspect of the presentinvention does not have any limitation in the material of the laminationmembers positioned on both end faces of the honeycomb structural body,which makes the two honeycomb structural bodies different from eachother.

However, since the first and second aspects of the present invention arein common with each other in that the honeycomb structural body is used,the following description will mainly discuss the honeycomb structuralbody of the first aspect of the present invention in which one of theends of each through hole is sealed so as to function as a collectingfilter, as the honeycomb structural body of the present invention. And,the limitation and the like of the position of the metal members and thehoneycomb structural body that does not have a structure in which one ofthe ends of each through hole is sealed will be described on demand inthe following description.

EFFECTS OF THE INVENTION

The honeycomb structural body (filter) of the present invention, whichhas a structure in which lamination members are laminated in the lengthdirection so that the through holes are superposed on one another, withone of the ends of each through hole being sealed, makes it possible toimprove the collecting efficiency. Moreover, since the flow of exhaustgases can be changed, deep-layer filtering processes in the inner sideof the wall portion can be executed so that the pressure loss afterparticulate collection is reduced.

Moreover, in the honeycomb structural body, upon regenerating process, agreat temperature difference occurs in the length direction of thefilter due to burning processes of particulates to cause a great thermalstress on the filter; however, the honeycomb structural body of thepresent invention has a structure in which lamination members arelaminated in the length direction so that, even when a great temperaturedifference occurs in the entire filter, a temperature differenceoccurring in each of the lamination members is comparatively small andthe resulting thermal stress is also small, thereby making the honeycombstructural body less likely to be damaged. Consequently, even continuousregenerating processes can be carried out on the honeycomb structuralbody of the present invention and thus the honeycomb structural body canbe used for a long time. Moreover, in the case where the filter isdesigned to have a complex shape, a uniform temperature response tendsto be disturbed to cause a temperature difference in the filter, makingthe filter very weak to the thermal stress; however, even when formedinto a complex shape, the honeycomb structural body of the presentinvention is less likely to be damaged.

Moreover, since the honeycomb structural body of the present inventionhas a structure in which lamination members are laminated in the lengthdirection, it is possible to freely change the amount of deposition ofthe catalyst in the length direction and the kind of the catalyst inaccordance with the application. Consequently, the honeycomb structuralbody of the present invention makes it possible to improve theregenerating process and purifying functions for toxic gases. In thiscase, it is not necessarily required to have the structure in which oneof the ends of each through hole is sealed in the honeycomb structuralbody.

Here, in the honeycomb structural body of the present invention, it ispossible to easily form irregularities on the surface of the wallportion of the honeycomb structural body by laminating laminationmembers having different shapes and/or sizes of the through holesalternately or at random. Thus, the irregularities formed on the surfaceof the wall portion make it possible to increase the filtering area andconsequently to reduce a pressure loss upon collecting particulates.Moreover, the irregularities allow the exhaust gas flow to form aturbulent flow so that the catalyst is effectively made in contact withtoxic gas components and particulates in exhaust gases; thus, it becomespossible to improve the purifying performance of exhaust gases and thepurifying rate for particulates upon regenerating process. Moreover, byforming the exhaust gas flow into a turbulent flow, it becomes possibleto reduce a temperature difference in the filter, and consequently toeffectively prevent damages due to thermal stress.

When the honeycomb structural body of the present invention is designedsuch that at least the lamination members positioned on both end facesof the honeycomb structural body are mainly made of metal, it ispossible to reduce wind erosion even after a long-term use. Moreover, itis possible to prevent occurrence of a gap to the casing (metalcontainer) and a gap between the respective lamination members at hightemperatures (during use) due to a difference in thermal expansion fromthat of the casing (metal container), and consequently to prevent a leakof particulates in exhaust gases and the subsequent reduction in thecollecting efficiency for particulates. Moreover, since the strength inthe end faces is increased, it becomes possible to prevent damages inthe filter due to exhaust gas pressure and the like imposed on the endfaces during use.

When all the lamination members of the honeycomb structural body of thepresent invention are mainly made of metal, a high porosity is achievedin the entire honeycomb structural body while realizing a low pressureloss, making it possible to ensure sufficient strength. Moreover, it ispossible to prevent occurrence of a gap to the casing (metal container)and a gap between the respective lamination members at high temperatures(during use) due to a difference in thermal expansion from that of thecasing (metal container). Moreover, since metal is superior in thermalconductivity, it is possible to improve the heat-averaging property, andconsequently to improve the purifying rate of particulates uponregenerating process. Furthermore, when a high porosity is achieved, thethermal capacity is reduced so that a quick temperature rise isavailable by the use of exhaust heat emitted from the internalcombustion engine; therefore, this structure is particularly beneficialwhen the filter is placed right under an engine so as to effectivelyutilize the exhaust heat.

When the honeycomb structural body of the present invention is designedto have sealed portions and the like, the honeycomb structural body isplaced in an exhaust gas purifying device or the like, and may be usedas a filter for purifying particulates.

In the present honeycomb structural body, when a catalyst is supportedon the lamination members, it can be used as a catalyst supportingmember to be used for purifying toxic gas components in exhaust gases inan exhaust gas purifying device and the like. Moreover, when thehoneycomb structural body of the present invention is also allowed tofunction as a filter for collecting particulates, it becomes possible toaccelerate the burning and removing processes of collected particulates.

BEST MODE FOR CARRYING OUT THE INVENTION

The honeycomb structural body of the first aspect of the presentinvention is a pillar-shaped honeycomb structural body having astructure in which a plurality of through holes are placed in parallelwith one another in the length direction with a partition wallinterposed therebetween, wherein lamination members are laminated in thelength direction so that the through holes are superposed on oneanother, and one of ends of each through hole is sealed.

The honeycomb structural body of the first aspect of the presentinvention also functions as a filter for collecting particulates, andwhen designed so that a catalyst is adhered to the through holes and thelike, it is allowed to function as a filter for collecting particulatesand a purifying device for toxic gases.

The honeycomb structural body of the second aspect of the presentinvention is a pillar-shaped honeycomb structural body having astructure in which a plurality of through holes are placed in parallelwith one another in the length direction with a partition wallinterposed therebetween, wherein lamination members are laminated in thelength direction so that the through holes are superposed on oneanother, and at least the lamination members positioned on both endfaces of the honeycomb structural body are mainly made of metal.

In the honeycomb structural body of the present invention, theabove-mentioned plurality of through holes may be formed by only normalthrough holes without sealed ends, or may include through holes with oneof ends being sealed (hereinafter, referred to as bottomed hole). In thecase where the through holes are designed to include bottomed throughholes, the honeycomb structural body of the present invention alsofunctions as a filter for collecting particulates, and in the case wheredesigned so that a catalyst is adhered to the through holes and thelike, it is allowed to function as a filter for collecting particulatesand a purifying device for toxic gases. Moreover, in the case where thethrough holes are formed by only the normal through holes, a catalyst isadhered to the through holes and the like so that the honeycombstructural body of the present invention is allowed to function as atoxic gas purifying device.

FIG. 1(a) is a perspective view that schematically shows a specificexample of a honeycomb structural body of the present invention, andFIG. 1(b) is a cross-sectional view taken along line A-A of FIG. 1(a).

A honeycomb structural body 10 is a cylindrical honeycomb structuralbody that has a structure in which a large number of through holes 11,each having one of ends being sealed, are placed in parallel with oneanother in the length direction with a partition wall interposedtherebetween.

In other words, as shown in FIG. 1(b), each of the bottomed holes 11 issealed at one of ends on its exhaust gas inlet side or outlet side sothat exhaust gases that have entered one bottomed hole 11 are dischargedfrom another bottomed hole 11 after having always passed through eachpartition wall 13 that separates the bottomed holes 11; thus, thepartition wall 13 is allowed to function as a filter.

As shown in FIG. 1, the honeycomb structural body of the presentinvention is a laminated member constituted by laminating laminationmembers 10 a each having a thickness of 0.1 to 20 mm, and the laminationmembers 10 a are laminated so that the through holes 11 are superposedon one another in the length direction.

Here, the expression, “lamination members are laminated so that throughholes are superposed on one another”, refers to the fact that thelamination is made so that through holes, formed in adjacent laminatedmembers, communicate with each other.

The lamination members may be mutually bonded to one another by using aninorganic bonding agent or the like, or may be simply laminatedphysically; however, it is preferable for the lamination members to besimply laminated physically. When they are simply laminated physically,it is possible to prevent a flow of exhaust gases from being interruptedby a joining portion made from the bonding agent and the like to causean increase in pressure losses. Here, in the case where the respectivelamination members are simply laminated physically, the laminationmembers need to be laminated in a casing (metallic cylindrical body) tobe attached to an exhaust pipe, and pressure is applied thereto.

As shown in FIG. 1, the honeycomb structural body of the presentinvention has a structure in which lamination members are laminated inthe length direction so that the through holes are superposed on oneanother, with one of the ends of each through hole being sealed. Thisstructure makes it possible to improve the collecting efficiency incomparison with the structure having no sealed portion. Moreover, adeep-layer filtering process can be carried out more easily. Themechanism for this has not been sufficiently clarified; however, it ispresumably explained as follows:

FIG. 9(a) is an enlarged cross-sectional view (see FIG. 1) thatschematically shows a wall portion 13 located between a through hole 11and another through hole 11 of the honeycomb structural body 10according to the present invention, and FIG. 9(b) is a cross-sectionalview (see FIG. 5) that schematically shows a wall portion 73 locatedbetween a through hole 71 and another through hole 71 of a honeycombstructural body 60 made of a ceramic material, which continuouslyextends in the length direction. Here, the horizontal direction of FIG.9 corresponds to the length direction of the honeycomb structural body.

In the honeycomb structural body 60 shown in FIG. 9(b), gas 66 isallowed to flow in various directions randomly through pores 73 blocated between particles 73 a, and since the honeycomb structural body10, shown in FIG. 9(a), has a structure in which lamination members 10 amade of porous members are laminated on one another, discontinuous facesexist between the particles 13 a and the pores 13 b. Consequently, thegas 16 flows while avoiding the discontinuous faces. In other words, thegas 16 tends to flow perpendicularly to the wall portion 13 so thatparticulates are deep-layer-filtered in the inner portion of the wall.For this reason, the pressure loss after collection of particulates isfurther lowered. Moreover, in the case where a catalyst used for burningparticulates is supported thereon, the possibility of contact betweenparticulates that have been deep-layer-filtered and the catalyst thathas been supported in the inner portion of the wall becomes higher,providing high burning efficiency for the catalyst.

Further, the honeycomb structural body has the structure in which thelamination members are laminated in the length direction; therefore,even when a great temperature difference occurs in the entire filterupon regenerating process, a temperature difference occurring in each ofthe lamination members is comparatively small and the resulting thermalstress is also small, thereby making the honeycomb structural body lesslikely to be damaged. Moreover, in the case where the filter is designedto have a complex shape, the filter tends to become very weak to thethermal stress; however, even when formed into a complex shape, thehoneycomb structural body of the present invention is less likely to bedamaged.

Moreover, all the lamination members, forming the honeycomb structuralbody of the present invention, may be formed by the same material, ormay be laminated by using members made from different materialscollectively, and although not particularly limited, at least thelamination members located on both of the end faces of the honeycombstructural body are mainly made of metal or ceramics preferably. Thehoneycomb structural body having such a structure is less likely to besuffered from wind erosion even after a long term use. In particular,when at least the lamination members located on both of the end faces ofthe honeycomb structural body are mainly made of metal, it is possibleto prevent occurrence of a gap to the casing (metal container) and a gapbetween the respective lamination members at high temperatures (duringuse) due to a difference in thermal expansion from that of the casing(metal container), and consequently to prevent a leak of particulates inexhaust gases and the subsequent reduction in the collecting efficiencyfor particulates. Moreover, since the strength in the end faces isincreased, it becomes possible to prevent damages in the filter due toexhaust gas pressure and the like imposed on the end faces during use,and consequently to carry out continuous regenerating processes.

As described above, with respect to the material for forming thelamination members, not particularly limited, for example, metals,porous ceramics, inorganic fibers and the like can be used.

In the case where metal is used as the material for forming thelamination members, with respect to the kinds of the metal, notparticularly limited, for example, chromium-based stainless,chromium-nickel-based stainless and the like may be used.

With respect to the above-mentioned metal, metal having a porousstructure is preferably used so as to allow the honeycomb structuralbody of the present invention to function as a filter.

In other words, the lamination member mainly made of metal is preferablyprepared as a structural body formed by three-dimensionally assembledmetal fibers made of the above-mentioned metal, or a structural bodymade of the above-mentioned metal with through pores being formed by apore-forming material, or a structural body formed by sintering metalpowder made of the above-mentioned metal in a manner so as to leavepores.

With respect to the porosity of the lamination members mainly made ofmetal, although not particularly limited, a preferable lower limit valueis set to 50% by volume and a preferable upper limit value is set to 98%by volume. The porosity of less than 50% by volume tends to fail tocarry out the deep-layer filtering process in the inner side of the wallportion, or causes degradation in the temperature raising property. Incontrast, the porosity exceeding 98% by volume tends to causedegradation in the strength of the lamination members mainly made ofmetal, and consequently makes the lamination members less likely to bedamaged. More preferably, the lower limit value is set to 70% by volumeand the upper limit value is set to 95% by volume.

Moreover, with respect to the average pore diameter of the laminationmembers mainly made of metal, although not particularly limited, apreferable lower limit value is set to 1 μm, and a preferable upperlimit value is set to 100 μm. The average particle size of less than 1μm tends to cause clogging in the inner side of the wall portion,failing to carry out the deep-layer filtering process. In contrast, theaverage particle size exceeding 100 μm makes particulates easily passthrough the pores to cause degradation in the particulate-collectingefficiency.

Here, the porosity and average particle diameter can be measured throughknown methods, such as measurements using a mercury porosimeter, aweighing method, Archimedes method and a measuring method using ascanning electronic microscope (SEM)

In the honeycomb structural body of the present invention, when all thelamination members are mainly made of metal, it becomes possible toensure sufficient strength even when the entire structure has a highporosity. Moreover, it becomes possible to effectively preventoccurrence of a gap to the casing (metal container) and a gap betweenthe respective lamination members at high temperatures (during use) dueto a difference in thermal expansion from that of the casing (metalcontainer) Furthermore, since the metal is superior in thermalconductivity, it is possible to improve the heat-averaging property, andconsequently to improve the purifying rate of particulates uponregenerating process. In addition, when a high porosity is achieved, thethermal capacity is reduced so that a quick temperature rise isavailable by using exhaust heat discharged from an internal combustionengine; therefore, this structure is particularly beneficial when thefilter is placed right under an engine so as to effectively utilize theexhaust heat.

Here, in the honeycomb structural body of the present invention, forexample, a structure may be adopted, in which several lamination membersmainly made of metal are respectively used on both of ends, withlamination members mainly made of inorganic fibers or lamination membersmainly made from a porous ceramic material being used in the center.

Moreover, these members may be properly combined with one another, orone of these materials may be used alone.

With respect to the material for the inorganic fibers forming thelamination members mainly made from inorganic fibers, examples thereofinclude oxide ceramics such as silica-alumina, mullite, alumina, silicaand the like, nitride ceramics such as aluminum nitride, siliconnitride, boron nitride, titanium nitride and the like and carbideceramics such as silicon carbide, zirconium carbide, titanium carbide,tantalum carbide, tungsten carbide and the like. Each of these may beused alone, or two or more kinds of these may be used in combination.

With respect to the fiber length of the inorganic fibers, a preferablelower limit value is set to 0.1 mm and a preferable upper limit value isset to 100 mm, more preferably, the lower limit value is set to 0.5 mmand the upper limit value is set to 50 mm. A preferable lower limitvalue of the inorganic fiber diameter is set to 1 μm, and a preferableupper limit value thereof is set to 30 μm, more preferably, the lowerlimit value is set to 2 μm and the upper limit value is set to 20 μm.

In addition to the above-mentioned inorganic fibers, the laminationmembers mainly made of inorganic fibers may contain a binder used forcombining the inorganic fibers with one another so as to maintain apredetermined shape.

With respect to the above-mentioned binder, not particularly limited,inorganic glass, such as silicate glass, silicate alkali glass andborosilicate glass, alumina sol, silica sol, titania sol and the likemay be used.

In case of including the binder, with respect to the content of thebinder, a preferable lower limit value is set to 5% by weight and apreferable upper limit value is set to 50% by weight; more preferably,the lower limit value is set to 10% by weight and the upper limit valueis set to 30% by weight; most preferably, the upper limit value is setto 20% by weight.

The lamination members, mainly made from inorganic fibers, may containinorganic particles and/or metal particles. With respect to the materialfor the inorganic particles, examples thereof include carbides, nitridesand oxides, and, specific examples thereof include silicon carbide,silicon nitride, boron nitride, alumina, silica, zirconia, titania andthe like. With respect to the material for the metal particles, examplesthereof include metallic silicon, aluminum, iron and titanium. Each ofthese may be used alone, or two or more kinds of these may be used incombination.

With respect to the apparent density of the lamination members mainlymade of inorganic fibers, a preferable lower limit value is set to 0.05g/cm³ and a preferable upper limit value is set to 1.00 g/cm³; morepreferably, the lower limit value is set to 0.10 g/cm³ and the upperlimit value is set to 0.50 g/cm³.

Moreover, with respect to the porosity of the lamination members mainlymade from inorganic fibers, a preferable lower limit value is set to 50%by volume and a preferable upper limit value is set to 98% by volume;and more preferably, the lower limit value is set to 60% by volume andthe upper limit value is set to 95% by volume, most preferably, thelower limit value is set to 80% by volume.

The porosity of not less than 50% allows particulates to penetrate thehoneycomb structural body deeper and consequently to be easily filtered;therefore, the catalyst deposited inside the wall and the particulatesare easily made in contact with each other to improve the reactivity.Here, the porosity exceeding 98% by volume tends to cause insufficientstrength.

Here, the apparent density can be measured through known methods, suchas a weighing method, Archimedes method and a measuring method using ascanning electronic microscope (SEM).

The lamination members mainly made from inorganic fibers may be easilyobtained through a paper-making method or the like.

With respect to the porous ceramic material for forming the laminationmembers mainly made from porous ceramics, examples thereof include:nitride ceramics such as aluminum nitride, silicon nitride, boronnitride and titanium nitride, carbide ceramics such as silicon carbide,zirconium carbide, titanium carbide, tantalum carbide and tungstencarbide, and oxide ceramics such as alumina, zirconia, cordieritemullite and silica. Moreover, the lamination members mainly made fromporous ceramics may be made from two or more kinds of materials, such asa composite of silicon and silicon carbide, and aluminum titanate.

With respect to the particle size of ceramic particles to be used uponmanufacturing the lamination members, although not particularly limited,those which are less likely to shrink in the succeeding firing processare preferably used, and for example, those particles, prepared bycombining 100 parts by weight of ceramic powder having an averageparticle size from 0.3 to 50 μm with 5 to 65 parts by weight of ceramicpowder having an average particle size from 0.1 to 1.0 μm, arepreferably used. By mixing ceramic powders having the above-mentionedrespective particle sizes at the above-mentioned blending ratio, it ispossible to manufacture the lamination members made from porousceramics.

With respect to the porosity of the lamination members mainly made fromporous ceramics, although not particularly limited, a preferable lowerlimit value is set to 50% by volume and a preferable upper limit valueis set to 80% by volume.

The porosity of less than 50% by volume fails to collect particulates inthe inner side of the wall portion; thus, the pressure loss tends torise abruptly upon collection of particulates; in contrast, the porosityexceeding 80% by volume causes degradation in the strength of thelamination members mainly made from porous ceramics; thus, it might beeasily broken.

Moreover, with respect to the average pore diameter of the laminationmembers mainly made from porous ceramics, although not particularlylimited, a preferable lower limit value is set to 1 μm, and a preferableupper limit value is set to 100 μm. The average particle size of lessthan 1 μm tends to cause clogging in the inner side of the wall portionand fail to carry out the deep-layer filtering process therein. Incontrast, the average particle size exceeding 100 μm makes particulateseasily pass through the pores to cause degradation in theparticulate-collecting efficiency.

In the honeycomb structural body of the present invention, a catalyst ispreferably supported on the lamination members 10 a.

When such a catalyst for purifying toxic gas components, such as CO, HCand NOx in exhaust gases, is supported thereon, the honeycomb structuralbody of the present invention is allowed to sufficiently purify thetoxic gas components in the exhaust gases through a catalytic reactionso that reaction heat, generated through the above-mentioned catalyticreaction, can be utilized for burning and removing particulates adheredto the wall portion 23. Moreover, when a catalyst used for reducingactivating energy of burning particulates is supported thereon, itbecomes possible to burn and remove the particulates more easily.

With respect to the catalyst to be supported on the honeycomb filter ofthe present invention, although not particularly limited, thosecatalysts which can reduce activating energy of burning particulates,and purify toxic gas components, such as CO, HC and NOx, in exhaustgases, are preferably used, and examples thereof include noble metals,such as platinum, palladium and rhodium, CeO₂ and oxides having aperovskite structure (LaCoO₃, LaMnO₃, etc.). Moreover, an element, suchas an alkali metal (Group 1 in Element Periodic Table), an alkali earthmetal (Group 2 in Element Periodic Table), a rare-earth element (Group 3in Element Periodic Table) and a transition metal element, may besupported thereon.

The above-mentioned catalyst may be supported on all the laminationmembers, or may be supported on only some of the lamination members. Forexample, in the case where the porosity of the respective laminationmembers is changed in accordance with the properties of the laminationmembers, the catalyst may be supported on only the lamination membersthat are allowed to have high porosity. In this manner, the honeycombstructural body of the present invention may be freely modified in theamount of deposition of the catalyst in the length direction as well asin the kind of the catalyst, in accordance with the application, so thatthe regenerating process and the purifying function for toxic gases canbe improved.

The above-mentioned catalyst may be supported on the surface of eachpore inside the wall portion 23, or may be supported on the wall portion23 with a certain thickness. Moreover, the catalyst may be supported onthe surface of the wall portion 23 and/or the surface of each poreuniformly, or may be supported on a certain fixed position in a biasedmanner. In particular, the catalyst is desirably supported on thesurface of the wall portion 23 inside the bottom hole 21 having anopening on the inlet side or on the surface of each pore in the vicinityof the surface, and is more desirably supported on both of theseportions. With these arrangements, the catalyst and the particulates aremade in contact with each other more easily, making it possible to carryout exhaust gas purifying processes more efficiently.

Moreover, when the catalyst of noble metal or the like is applied to thehoneycomb structural body of the present invention, it is preferable toapply the catalyst after the surface has been preliminarily coated witha support material such as alumina. This arrangement makes the specificsurface area greater to enhance the dispersion degree of the catalystand increase the reactive portions of the catalyst. Moreover, since thesupport material prevents the catalyst metal from sintering, the heatresistance of the catalyst is improved.

When such a catalyst is supported thereon, the honeycomb structural bodyof the present invention is allowed to function as a filter capable ofcollecting particulates in exhaust gases, and also to function as acatalyst-supporting member for purifying CO, HC, NOx and the likecontained in exhaust gases.

Here, the honeycomb structural body of the present invention in whichthe catalyst is supported is allowed to function as a gas purifyingdevice in the same manner as the conventionally known DPFs (DieselParticulate Filters) with catalyst. Therefore, the detailed explanationof the functions as the catalyst-supporting member of the honeycombstructural body of the present invention is omitted.

With respect to the porosity of the honeycomb structural body as a wholeof the present invention, although not particularly limited, apreferable lower limit value is set to 50% by volume and a preferableupper limit value is set to 98% by volume and more preferably, the lowerlimit value is set to 60% by weight and the upper limit value is set to95% by weight. Most preferably, the lower limit value is set to 80% byvolume.

With respect to the thickness of the wall portion, a preferable lowerlimit value is set to 0.2 mm and a preferable upper limit value is setto 10.0 mm; more preferably, the lower limit value is set to 0.3 mm andthe upper limit value is set to 6.0 mm.

With respect to the density of through holes on a cross sectionperpendicular to the length direction of the honeycomb structural body,although not particularly limited, a preferable lower limit value is setto 0.16 piece/cm² (1.0 piece/in²) and a preferable upper limit value isset to 62 pcs/cm² (400 pcs/in²); more preferably, the lower limit valueis set to 0.62 piece/cm² (4.0 pcs/in²) and the upper limit value is setto 31 pcs/cm² (200 pcs/in²).

Here, with respect to the size of the through hole on a cross sectionperpendicular to the length direction of the honeycomb structural body,although not particularly limited, a preferable lower limit value is setto 1.4 mm×1.4 mm, and a preferable upper limit value is set to 16 mm×16mm.

Moreover, lamination members with holes having different sizes areprepared, and when these members are laminated successively,irregularities are formed on the inner surface of each through hole sothat the through hole having a larger surface area is formed. Therefore,the filtering area is increased and it is possible to reduce a pressureloss upon collecting particulates. Moreover, the irregularities allowthe exhaust gas flow to form a turbulent flow so that the catalyst iseffectively made in contact with toxic gas components and particulatesin the exhaust gases; thus, it becomes possible to improve the purifyingperformance of exhaust gases and the purifying rate for particulatesupon regenerating process. Moreover, by forming the exhaust gas flowinto a turbulent flow, it becomes possible to reduce a temperaturedifference in the filter, and consequently to effectively preventdamages due to thermal stress. With respect to the shape of the hole,not particularly limited to a quadrangular shape, for example, anydesired shapes, such as a triangle, a hexagon, an octagon, a dodecagon,a round shape and an elliptical shape, may be used.

A honeycomb structural body 10, shown in FIG. 1, has a cylindricalshape; however, not particularly limited to the cylindrical shape, thehoneycomb structural body of the present invention may have any desiredpillar shape, such as an elliptical cylindrical shape and a rectangularpillar shape, with any desired size.

Moreover, in the case where the filter is installed right under theengine, the filter space is extremely limited, and a complex filtershape is required. However, in the case of the honeycomb structural bodyof the present invention, even a complex shape, such as a filter 30 witha concave portion on one side as shown in FIG. 6(a) and a filter 40 withconcave portions on both sides as shown in FIG. 6(b), can be easilyformed by superposing lamination members 30 a or 40 a in the lengthdirection. Moreover, since the honeycomb structural body of the presentinvention is formed by laminating the lamination members in the lengthdirection, even a curved shape in the length direction and a deformedshape that is gradually changed in the length direction can be easilyformed.

Referring to FIG. 2, the following description will discuss a sequenceof processes of one example of the manufacturing method for thehoneycomb structural body of the present invention.

(1) Manufacturing Method for Lamination Members Mainly Made of Metal

First, a porous metal plate having a thickness of 0.1 to 20 mm, mainlymade of metal, is machined by laser so that holes are formed on thealmost entire surface with almost the same intervals from each other;thus, a lamination member 10 a having a honeycomb shape with throughholes in high density is formed.

Moreover, in the case where a lamination member, which is placed near anend face of the honeycomb structural body of the present invention so asto form a sealing portion with bottomed holes, is manufactured, uponlaser machining process, a honeycomb-shape lamination member 10 b inwhich the holes are formed in a staggered pattern with through holesformed in a lower density is manufactured.

In other words, by using several sheets of these lamination members 10 bto form an end portion, it is possible to prepare a honeycomb structuralbody capable of functioning as a filter without the necessity of sealingpredetermined through holes at the end portion.

Next, an alumina film having a large specific surface area is formed onthe surface of the above-mentioned lamination member 10 a or 10 b, and acatalyst such as platinum is applied to the surface of this aluminafilm. This process is of course unnecessary when a lamination membermainly made of metal having no catalyst deposited thereon ismanufactured.

With respect to the method for forming the alumina film on the surfaceof the lamination member 10 a or 10 b, for example, a method in whichthe lamination member 10 a or 10 b is impregnated with a solution of ametal compound containing aluminum such as Al(NO₃)₃, and heated, and amethod in which the lamination member 10 a or 10 b is impregnated with asolution containing alumina powder, and heated, are proposed.

With respect to the method for applying a co-catalyst or the like to thealumina film, for example, a method in which the lamination member 10 aor 10 b is impregnated with a solution of a metal compound containing arare-earth element such as Ce(NO₃)₃, and heated is proposed.

With respect to the method for applying a catalyst to the alumina film,for example, a method in which the lamination member 10 a or 10 b isimpregnated with a solution of dinitrodiammine platinum nitrate([Pt(NH₃)₂(NO₂)₂]HNO₃), and heated is proposed.

As described above, the honeycomb structural body of the presentinvention is preferably made of only a lamination member mainly made ofmetal, however in addition to this, a lamination member mainly made frominorganic fibers, a lamination member mainly made from ceramics and thelike may be included therein.

(2) Manufacturing Method for Lamination Members Mainly Made fromInorganic Fibers

First, preferably, a catalyst made from noble metal such as platinum ispreliminarily applied to inorganic fibers such as alumina fibers thatform a constituent material. By applying the catalyst to the inorganicfibers before the forming process, it is possible to apply the catalystin a more uniformly dispersed state. This process is of courseunnecessary when a lamination member mainly made from inorganic fibershaving no catalyst deposited thereon is manufactured.

With respect to the method for applying the catalyst to the inorganicfibers, for example, a method in which inorganic fibers have beenimpregnated in a slurry of an oxide on which a catalyst is supported,the fibers are taken out and heated, and a method in which afterinorganic fibers have been impregnated with a slurry containing acatalyst, the fibers are taken out and heated, are proposed. In thelatter method, the catalyst is directly adhered to the inorganic fibers.

Here, with respect to the amount of deposition of the catalyst, apreferable lower limit value is set to 0.01 g/10 g of inorganic fibers,and a preferable upper limit value is set to 1 g/10 g of inorganicfibers.

In this manner, in the case of lamination members mainly made frominorganic fibers, since the catalyst is directly applied to theinorganic fibers that are a constituent material prior to the formingprocess, it is possible to apply the catalyst in a more uniformlydispersed state. Here, the application of the catalyst may be carriedout after a paper-making process, which will be described later.

Next, a slurry for paper-making is prepared.

More specifically, the inorganic fibers bearing the catalyst, obtainedthrough the above-mentioned method, were dispersed in water (1 L) at arate of 5 to 100 g, and in addition to these, 10 to 40 parts by weightof an inorganic binder such as silica sol and 1 to 10 parts by weight ofan organic binder were added to 100 parts by weight of the inorganicfibers, and to this were further added a slight amount of a coagulationagent such as aluminum sulfate and an aggregation agent such aspolyacrylic amide, if necessary, and sufficiently stirred to prepare aslurry for paper-making.

With respect to the above-mentioned organic binder, not particularlylimited, for example, acrylic latex, methylcellulose,carboxymethylcellulose, hydroxyethylcellulose, polyethylene glycol,phenol resin, epoxy resin, polyvinyl alcohol and styrene-butadienerubber may be used.

Next, lamination members mainly made from inorganic fibers are subjectedto a paper-making process by using the slurry for paper-making.

More specifically, the slurry for paper-making was subjected to apaper-making process by using a perforated mesh in which holes having apredetermined shape were formed with mutually predetermined intervals,and the resulting matter was dried at a temperature in a range from 100to 200° C. so that a honeycomb-shape lamination member 10 a, which hadthrough holes and a predetermined thickness as shown in FIG. 2(a), wasobtained.

Moreover, in the case where a lamination member that is placed near anend face of the honeycomb structural body of the present invention, andforms a sealing portion with bottomed holes is manufactured, by using,for example, a mesh having holes with a predetermined shape that areformed in a staggered pattern is used so that a honeycomb-shapelamination member 10 b mainly made from inorganic fibers, which has apredetermined thickness with through holes formed therein in a lowerdensity, is prepared.

Here, through the above-mentioned paper-making process, theabove-mentioned inorganic fibers are aligned almost in parallel with themain face of the lamination member, and when the lamination body hasbeen formed, more of the inorganic fibers are aligned along the faceperpendicular to the forming direction of the through holes incomparison with those aligned along the horizontal face with respect tothe forming direction of the through holes. Therefore, since thehoneycomb structural body of the present invention allows exhaust gasesto pass through the wall portion more easily, it is possible to reducethe initial pressure loss, and also to allow particulates to passthrough deeper layers inside the wall portion; consequently, it becomespossible to prevent formation of cake layers on the surface of the wallportion, and consequently to suppress an increase in the pressure lossupon collecting particulates. Moreover, since the rate of exhaust gasesflowing in parallel with the aligned direction of the inorganic fibersincreases, the chance of the particulates coming into contact with thecatalyst adhered to the inorganic fibers increases, making it possibleto easily burn the particulates.

Furthermore, as in the case of the present invention, when thelamination members are prepared as laminated layers, the above-mentionedeffects are further improved.

(3) Manufacturing Method for Lamination Members Mainly Made fromCeramics

First, by using the above-mentioned material paste mainly composed ofceramics, a ceramic formed body having almost the same shape as adesired lamination member is manufactured through a molding method suchas an extrusion-molding method, a press-molding method and the like.

With respect to the material paste, although not particularly limited,those which maintain the porosity of the lamination member in a rangefrom 50 to 80% by volume after the manufacturing process are preferablyused, and, for example, a material, prepared by adding a binder, adispersant solution and the like to the above-mentioned powder made fromceramics, may be used.

With respect to the binder, not particularly limited, for example,methylcellulose, carboxy methylcellulose, hydroxy ethylcellulose,polyethylene glycol, phenolic resin, epoxy resin and the like may beused.

Normally, the amount of blend of the binder is preferably set in a rangefrom 1 to 10 parts by weight with respect to 100 parts by weight ofceramic powder.

With respect to the dispersant solution, not particularly limited, forexample, an organic solvent such as benzene, alcohol such as methanoland water may be used.

An appropriate amount of the above-mentioned dispersant solution ismixed therein so that the viscosity of the material paste is set withina fixed range.

These ceramic powder, binder and dispersant solution are mixed by anattritor or the like, and sufficiently kneaded by a kneader or the like,and then molded.

Moreover, a molding auxiliary may be added to the material paste, ifnecessary.

With respect to the molding auxiliary, not particularly limited,examples thereof include: ethylene glycol, dextrin, fatty acid soap,polyalcohol and the like.

Furthermore, a pore-forming agent, such as balloons that are fine hollowspheres composed of oxide-based ceramics, spherical acrylic particlesand graphite, may be added to the above-mentioned material paste, ifnecessary.

With respect to the above-mentioned balloons, not particularly limited,for example, alumina balloons, glass micro-balloons, shirasu balloons,fly ash balloons (FA balloons) and mullite balloons may be used. Amongthese, fly ash balloons are more preferably used.

Next, after the above-mentioned ceramic formed body has been dried byusing a drier such as a microwave drier, a hot-air drier, a dielectricdrier, a reduced-pressure drier, a vacuum drier and a frozen drier, theresulting ceramic dried body is subjected to degreasing and firingprocesses under predetermined conditions.

Here, with respect to the degreasing and firing conditions and the likeof the ceramic dried body, it is possible to apply conditions that havebeen conventionally used for manufacturing a filter made from porousceramics.

Next, in the same manner as the lamination member mainly made of metal,an alumina film having a large specific surface area is formed on thesurface of the ceramic fired body obtained through a firing process, anda catalyst such as platinum is applied to the surface of this aluminafilm. This process is of course unnecessary when a lamination membermainly made from ceramics having no catalyst deposited thereon ismanufactured.

(4) Laminating Process of Lamination Members

By using a cylindrical casing 23 (metal container) having a pressingmember on one side as shown in FIG. 2(b), several lamination members forend-use 10 b, manufactured through processes (1) to (3), are laminatedinside the casing 23, and a predetermined number of the inside-uselamination members 10 a are then laminated therein. Then, severallamination members for end-use 10 b are lastly laminated thereon, andafter having been pressed, another pressing member is also put on theother side and secured thereon so that a honeycomb structural body thathas been subjected to a canning process is prepared. In this process, ofcourse, the lamination members 10 a and 10 b are laminated so that thethrough holes are superposed on one another.

With respect to the application of the honeycomb structural body of thefirst and second aspects of the present invention, although notparticularly limited, it is preferably used for exhaust gas purifyingdevices for use in vehicles.

FIG. 3 is a cross-sectional view that schematically shows one example ofan exhaust gas purifying device for use in vehicles, which is providedwith the honeycomb structural body of the present invention.

As shown in FIG. 3, an exhaust gas purifying device 200 is mainlyconstituted by a honeycomb structural body 20 of the present invention,and a casing 23 that covers the external portion of the honeycombstructural body 20; and an introducing pipe 24 that is connected to aninternal combustion system such as an engine is connected to the end ofthe casing 23 on the side to which exhaust gases are directed, and anexhaust pipe 25 externally coupled is connected to the other end of thecasing 23. Here, in FIG. 3, arrows indicate flows of exhaust gases.

In the exhaust gas purifying device 200 having the above-mentionedarrangement, exhaust gases, discharged from the internal combustionsystem such as an engine, are introduced into the casing 23 through theintroducing pipe 24, and allowed to pass through the wall portion fromthe bottomed hole of the honeycomb structural body 20; thus, the exhaustgases are purified, with particulates thereof being collected in thewall portion, and are then discharged outside through the exhaust pipe25.

After a large quantity of particulates have been accumulated on the wallportion of the honeycomb structural body 20 to cause an increase inpressure loss, the honeycomb structural body 20 is subjected to aregenerating process.

The regenerating process of the honeycomb structural body 20 means thatthe collected particulates are burned. With respect to the regeneratingmethod for the honeycomb structural body of the present invention, forexample, the following methods are used: a method in which the honeycombstructural body is heated by using a heating means placed on the exhaustgas inlet side, a method in which an oxidizing catalyst is deposited onthe honeycomb structural body, and hydrocarbon and the like of exhaustgases are oxidized by this oxidizing catalyst to generate heat so thatby utilizing this heat, the regenerating process is carried out inparallel with the exhaust gas purifying process, a method in which acatalyst, which directly oxidizes solid-state particulates, is attachedto the filter, and a method in which NOx is oxidized by using anoxidizing catalyst placed on the upstream side of the honeycombstructural body to generate NO₂ so that particulates are oxidized byusing the NO₂.

EXAMPLES

The following description will discuss the present invention in detailby means of examples; however, the present invention is not intended tobe limited by these examples.

Example 1

(1) Manufacturing Process of Lamination Members

A three-dimensional mesh-shape porous member, made of Ni—Cr alloy (tradename: CELMET, average pore diameter: 400 μm, made by Sumitomo ElectricIndustries Ltd.), was compressed by a roller so as to have an averagepore diameter of 80 μm, and after having been machined into a disc shapehaving a size of 43.8 mm in diameter×1 mm in thickness, the resultingdisc is machined by laser to form holes, each having a size of 6 mm×6mm, over the almost entire surface with mutual intervals of 2 mm; thus,a lamination member A₁ having a honeycomb shape was manufactured.

Moreover, in order to form members for use in two end portions of thehoneycomb structural body, a three-dimensional mesh-shape porous member,made of Ni—Cr alloy (trade name: CELMET, average pore diameter: 400 μm,made by Sumitomo Electric Industries Ltd.), was compressed by a rollerso as to have an average pore diameter of 80 μm, and after having beenmachined into a disc shape having a size of 143.8 mm in diameter×1 mm inthickness, the resulting disc is machined by laser so that a laminationmember B₁ in which holes, each having a size of 6 mm×6 mm, are formed ina staggered pattern was prepared.

(2) Catalyst Applying Process

Al(NO₃)₃ was put into 1,3-butane diol, and the resulting solution wasstirred at 60° C. for 5 hours to prepare a 1,3-butane diol solutioncontaining 30% by weight of Al(NO₃)₃. After the lamination members A₁and B₁ had been immersed in this 1,3-butane diol solution, these wereheated at 150° C. for 2 hours, and then heated at 400° C. for 2 hours,and after having been immersed in water at 80° C. for 2 hours, thesewere heated at 700° C. for 8 hours so that an alumina layer was formedon the surface of each of the lamination members A₁ and B₁ at a rate of60 g/l.

Ce(NO₃)₃ was charged into ethylene glycol, and the resulting solutionwas stirred at 90° C. for 5 hours to prepare an ethylene glycol solutioncontaining 6% by weight of Ce(NO₃)₃. After the lamination members A₁ andB₁ bearing the alumina layers formed thereon had been immersed in thisethylene glycol solution, these were heated at 150° C. for 2 hours, andthen heated at 650° C. for 2 hours in a nitrogen atmosphere; thus, analumina layer containing a rare-earth oxide, used for bearing a catalyston the surface thereof, was formed on the surface of each of thelamination members A₁ and B₁.

After the lamination members A₁ and B₁ bearing the alumina layerscontaining a rare-earth oxide formed thereon had been immersed in adinitrodiammine platinum nitrate ([Pt(NH₃)₂(NO₂)₂]HNO₃) aqueoussolution, these were heated at 110° C. for 2 hours, and then heated at500° C. for 1 hour in a nitrogen atmosphere; thus, a platinum catalysthaving an average particle size of 2 nm was deposited on the surface ofeach of the lamination members A₁ and B₁ at a rate of 5 g/l.

(3) Laminating Process

A casing (cylindrical metal container) having a pressing member on oneside was placed with the side to which the pressing member was attachedfacing down. After five of the lamination members B₁ bearing theplatinum catalyst deposited thereon had been laminated, 140 of thelamination members A₁ bearing the platinum catalyst deposited thereonwere laminated, and five of the lamination members B₁ bearing theplatinum catalyst deposited thereon were lastly laminated thereon;moreover, this was then subjected to a pressing process, and a pressingmember was also placed on the other side so as to be secured so that anexhaust gas purifying device in which a honeycomb structural body havinga length of 150 mm was assembled into a casing was prepared. Here, inthis process, the respective lamination members were laminated so thatthe through holes were superposed on one another.

Example 2

A three-dimensional mesh-shape porous member, made of Ni—Cr alloy (tradename: CELMET, average pore diameter: 400 μm, made by Sumitomo ElectricIndustries Ltd.), was compressed by a roller so as to have an averagepore diameter of 80 μm, and after having been machined into a disc shapehaving a size of 143.8 mm in diameter×1 mm in thickness, the resultingdisc is machined by laser to manufacture a lamination member A₂ having ahoneycomb shape with a thickness of 2 mm in the same manner as thelamination member A₁; then, the same processes as Example 1 were carriedout except that after having applied a catalyst thereto, five of thelamination members B₁, 70 of the lamination members A₂ and five of thelamination members B₁ were laminated in this order so that an exhaustgas purifying device in which a honeycomb structural body having alength of 150 mm was assembled into a casing was prepared.

Example 3

A three-dimensional mesh-shape porous member, made of Ni—Cr alloy (tradename: CELMET, average pore diameter: 400 μm, made by Sumitomo ElectricIndustries Ltd.), was compressed by a roller so as to have an averagepore diameter of 80 μm, and after having been machined into a disc shapehaving a size of 143.8 mm in diameter×4 mm in thickness, the resultingdisc is machined by laser to manufacture a lamination member A₃ having ahoneycomb shape with a thickness of 4 mm in the same manner as thelamination member A₁; then, the same processes as Example 1 were carriedout except that after having applied a catalyst thereto, five of thelamination members B₁, 35 of the lamination members A₃ and five of thelamination members B₁ were laminated in this order so that an exhaustgas purifying device in which a honeycomb structural body having alength of 150 mm was assembled into a casing was prepared.

Example 4

The same processes as those of Example 1 were carried out to produce 70lamination members A₁, and 70 lamination members A₄ that were the sameas the lamination members A₁ except that the size of the holes was setto 4 mm×4 mm with mutual intervals between the holes being set to 4 mmwere produced; then, the same processes as Example 1 were carried outexcept that after having applied a catalyst thereto, five of thelamination members B₁, 140 members, formed by alternately placing thelamination members A₁ and the lamination members A₄, and five of thelamination members B₁ were laminated in this order so that an exhaustgas purifying device in which a honeycomb structural body having alength of 150 mm was assembled into a casing was prepared.

Example 5

(1) Catalyst Applying Process to Inorganic Fibers

Alumina fibers (average fiber diameter: 5 μm, average fiber length: 0.3mm) were impregnated with an alumina slurry bearing Pt (Ptconcentration: 5% by weight) for two minutes, and then heated at 500° C.to prepare alumina fibers to which the catalyst is adhered. The amountof deposition of Pt was 0.24 g/10 g of alumina.

(2) Preparation Process for Slurry for Paper-Making

Next, the alumina fibers obtained from the process (1) were dispersed inwater (1 L) at a rate of 10 g, and in addition to these, 5% by weight ofsilica sol serving as an inorganic binder and 3% by weight of an acryliclatex serving as an organic binder were added to the fibers. Further, aslight amount of aluminum sulfate serving as a coagulation agent andpolyacrylic amide serving as an aggregation agent were further addedthereto, and the mixture was sufficiently stirred to prepare a slurryfor paper-making.

(3) Paper-Making Process

The slurry for paper-making, obtained in the process (2), was subjectedto a paper-making process by using a perforated mesh having a diameterof 143.8 mm in which holes having a size of 6 mm×6 mm were formed overthe entire surface with mutual intervals of 2 mm, and the resultingmatter was dried at a temperature of 150° C. so that a lamination memberA₅ having a size of 143.8 mm in diameter×1 mm in thickness with holes of6 mm×6 mm being formed on the almost entire surface with mutualintervals of 2 mm was prepared.

(4) Laminating Process

A casing (cylindrical metal container) having a pressing member on oneside was placed with the side to which the pressing member was attachedfacing down. After five of the lamination members B₁ manufactured in thesame manner as Example 1 had been laminated, 150 sheets of thelamination members A₅ were laminated, and five of the lamination membersB₁ manufactured in the same manner as Example 1 were lastly laminatedtherein, and this was further subjected to a pressing process, andanother pressing member was also put on the other side so as to besecured so that an exhaust gas purifying device in which a honeycombstructural body having a length of 150 mm was assembled into a casingwas prepared. The amount of Pt deposition of this honeycomb structuralbody was 5 g/l. Here, in this process, the respective lamination memberswere laminated so that the through holes were superposed on one another.

Example 6

The same processes as those of Example 2 were carried out except thatafter having produced a lamination member A₆ having the same compositionand the same shape as the lamination member A₅ with a thickness of 5 mm,five of the lamination members B₁, 30 of the lamination members A₆ andfive of the lamination members B₁ were laminated in this order so thatan exhaust gas purifying device in which a honeycomb structural bodyhaving a length of 150 mm was assembled into a casing was prepared.

Example 7

The same processes as those of Example 3 were carried out except thatafter having produced a lamination member A₇ having the same compositionand the same shape as the lamination member A₅ with a thickness of 10mm, five of the lamination members B₁, 15 of the lamination members A₇and five of the lamination members B₁ were laminated in this order sothat an exhaust gas purifying device in which a honeycomb structuralbody having a length of 150 mm was assembled into a casing was prepared.

Example 8

The same processes as those of Example 5 were carried out to produce 75lamination members A₅, and 75 lamination members A₈ that were the sameas the lamination members A₅ except that the size of the holes was setto 4 mm×4 mm with mutual intervals between the holes being set to 4 mmwere produced; then, the same processes as Example 5 were carried outexcept that after having applied a catalyst thereto, five of thelamination members B₁, 150 members, formed by alternately placing thelamination members A₅ and the lamination members A₈, and five of thelamination members B₁ were laminated in this order so that an exhaustgas purifying device in which a honeycomb structural body having alength of 150 mm was assembled into a casing was prepared.

Example 9

(1) Manufacturing Process of Lamination Members

A metal fiber porous member, made of Ni—Cr—Mo based stainless (SUS316L:trade name: NASLON, made by Nippon Seisen Co., Ltd.), was machined intoa disc shape having a size of 143.8 mm in diameter×1 mm in thickness,and the resulting disc is machined by laser to form holes, each having asize of 6 mm×6 mm, over the almost entire surface with mutual intervalsof 2 mm; thus, a lamination member A₉ having a honeycomb shape wasmanufactured.

Moreover, in order to form members for use in two end portions of thehoneycomb structural body, a metal fiber porous member, made of Ni—Cr—Mobased stainless (SUS316L: trade name: NASLON, made by Nippon Seisen Co.,Ltd.), was machined into a disc shape having a size of 143.8 mm indiameter×1 mm in thickness, and the resulting disc is machined by laserso that a lamination member B₂ having holes, each having a size of 6mm×6 mm, in a staggered pattern.

(2) Catalyst Applying Process

The same processes as Example 1 were carried out so that an aluminalayer containing a rare-earth oxide was formed on each of the laminationmembers A₉ and B₂ with 5 g/l of platinum catalyst having an averageparticle size of 2 nm being deposited thereon.

(3) Laminating Process

A casing (cylindrical metal container) having a pressing member on oneside was placed with the side to which the pressing member was attachedfacing down. After five of the lamination members B₂ bearing theplatinum catalyst deposited thereon had been laminated, 140 of thelamination members A₉ bearing the platinum catalyst deposited thereonwere laminated, and five of the lamination members B₂ bearing theplatinum catalyst deposited thereon were lastly laminated therein, andthis was further subjected to a pressing process, and another pressingmember was also put on the other side so as to be secured so that anexhaust gas purifying device in which a honeycomb structural body havinga length of 150 mm was assembled into a casing was prepared. In thisprocess, the lamination members were laminated so that the through holesare superposed on one another. Here, in this process, the respectivelamination members were laminated so that the through holes weresuperposed on one another.

Example 10

The same processes as those of Example 1 were carried out to produce 140lamination members A₁, and the same processes as those of Example 9 werecarried out to produce ten lamination members B₂; then, the sameprocesses as Example 1 were carried out except that after having applieda catalyst thereto, five of the lamination members B₂, 140 of thelamination members A₁ and five of the lamination members B₂ werelaminated in this order so that an exhaust gas purifying device in whicha honeycomb structural body having a length of 150 mm was assembled intoa casing was prepared.

Example 11

(1) Catalyst Applying Process to Inorganic Fibers

Alumina fibers (average fiber diameter: 5 μm, average fiber length: 0.3mm) were impregnated with an alumina slurry bearing Pt (Ptconcentration: 5% by weight) for two minutes, and then heated at 500° C.to prepare alumina fibers to which the catalyst is adhered. The amountof deposition of Pt was 0.24 g/10 g of alumina.

(2) Preparation Process for a Slurry for Paper-Making

Next, the alumina fibers obtained from the process (1) were dispersed inwater (1 L) at a rate of 10 g, and in addition to these, 5% by weight ofsilica sol serving as an inorganic binder and 3% by weight of an acryliclatex serving as an organic binder were added to the fibers. Further, aslight amount of aluminum sulfate serving as a coagulation agent andpolyacrylic amide serving as an aggregation agent were further addedthereto, and the mixture was sufficiently stirred to prepare a slurryfor paper-making.

(3) Paper-Making Process

The slurry, obtained in the process (2), was subjected to a paper-makingprocess by using a perforated mesh having a diameter of 143.8 mm inwhich holes having a size of 6 mm×6 mm were formed over the entiresurface with mutual intervals of 2 mm, and the resulting matter wasdried at a temperature of 150° C. so that a lamination member A₁₀ havinga thickness of 1 mm with holes of 6 mm×6 mm being formed on the entiresurface with mutual intervals of 2 mm was prepared.

Moreover, in order to form members for use in two end portions of thehoneycomb structural body, the paper-making and drying processes werecarried out in the same manner by using a mesh in which holes having asize of 6 mm×6 mm were formed in a staggered pattern so that alamination member B₃ having a thickness of 1 mm with holes of 6 mm×6 mmbeing formed in the staggered pattern was prepared.

(4) Laminating Process

A casing (cylindrical metal container) having a pressing member on oneside was placed with the side to which the pressing member was attachedfacing down. After five of the lamination members B₃ had been laminated,140 of the lamination members A₁₀ were laminated, and five of thelamination members B₃ were lastly laminated therein, and this wasfurther subjected to a pressing process, and another pressing member wasalso put on the other side so as to be secured so that a honeycombstructural body having a length of 150 mm, made of a laminated body, wasprepared. The amount of Pt deposition of this honeycomb structural bodywas 5 g/l.

Here, in this process, the respective lamination members were laminatedso that the through holes were superposed on one another.

Example 12

(1) Preparation Process for a Slurry for Paper-Making

Alumina fibers (average fiber diameter: 5 μm, average fiber length: 0.3mm) were dispersed in water (1 L) at a rate of 10 g, and in addition tothese, 5% by weight of silica sol serving as an inorganic binder and 3%by weight of an acrylic latex serving as an organic binder were added tothe fibers. Further, a slight amount of aluminum sulfate serving as acoagulation agent and polyacrylic amide serving as an aggregation agentwere further added thereto, and the mixture was sufficiently stirred toprepare a slurry for paper-making.

(2) Paper-Making Process

The slurry for paper-making, obtained in the process (1), was subjectedto a paper-making process by using a perforated mesh having a diameterof 143.8 mm in which holes having a size of 6 mm×6 mm were formed overthe entire surface with mutual intervals of 2 mm, and the resultingmatter was dried at a temperature of 150° C. so that a lamination memberA₁₁ having a size of 143.8 mm in diameter×1 mm in thickness with holesof 6 mm×6 mm being formed on the almost entire surface with mutualintervals of 2 mm was prepared. Moreover, in order to obtain sheets foruse in two end portions of the honeycomb structural body, thepaper-making and drying processes were carried out in the same manner byusing a mesh in which holes having a size of 6 mm×6 mm were formed in astaggered pattern so that a lamination member B₄ having a thickness of 1mm with holes of 6 mm×6 mm being formed in the staggered pattern wasprepared.

(3) Catalyst Applying Process

Next, 0.01 mole of La(NO₃)₃.6H₂O, 0.01 mole of Co(OCOCH₃)₂.4H₂O and0.024 mole of C₆H₈O₇.H₂O(citric acid) were mixed and stirred in 20 ml ofan ethanol solvent to prepare LaCoO₃ precursor sol. The laminationmembers A₁₁ and B₄ were impregnated with this precursor sol, and afterhaving been taken out, extra sol was removed by a suction process, andthe resulting matter was dried at 100° C., and fired at 600° C. for onehour so that a lamination member A₁₂ and a lamination member B₅ wereobtained. Here, the perovskite structure of LaCoO₃ was confirmed throughX-ray diffraction measurements. The amount of deposition of the catalystwas 30 g/l.

(4) Laminating Process

A casing (cylindrical metal container) having a pressing member on oneside was placed with the side to which the pressing member was attachedfacing down. After five of the lamination members B₅ had been laminated,140 of the lamination members A₁₂ were laminated, and five of thelamination members B₅ were lastly laminated thereon; moreover, this wasthen subjected to a pressing process, and a pressing member was alsoplaced on the other side so as to be secured so that a honeycombstructural body made of a laminated body having a length of 150 mm wasprepared.

Here, in this process, the respective lamination members were laminatedso that the through holes were superposed on one another.

Example 13

(1) Catalyst Applying Process

Further, 0.01 mole of La(NO₃)₃.6H₂O, 0.01 mole of Co(OCOCH₃)₂.4H₂O and0.024 mole of C₆H₈O₇.H₂O(citric acid) were mixed and stirred in 20 ml ofan ethanol solvent to prepare LaCoO₃ precursor sol. The laminationmembers A₁ and B₁ were impregnated with this precursor sol, and afterhaving been taken out, extra sol was removed by a suction process, andthe resulting matter was dried at 100° C., and fired at 600° C. for onehour so that a lamination member A₁₃ and a lamination member B₆ wereobtained. Here, the perovskite structure of LaCoO₃ was confirmed throughX-ray diffraction measurements. The amount of deposition of the catalystwas 30 g/l.

(2) Laminating Process

A casing (cylindrical metal container) having a pressing member on oneside was placed with the side to which the pressing member was attachedfacing down. After five of the lamination members B₆ had been laminated,140 of the lamination members A₁₃ were laminated, and five of thelamination members B₆ were lastly laminated thereon; moreover, this wasthen subjected to a pressing process, and a pressing member was alsoplaced on the other side so as to be secured so that a honeycombstructural body made of a laminated body having a length of 150 mm wasprepared.

Here, in this process, the respective lamination members were laminatedso that the through holes were superposed on one another.

Example 14

(1) Catalyst Applying Process

Moreover, 0.01 mole of La(NO₃)₃.6H₂O, 0.01 mole of Co(OCOCH₃)₂.4H₂O and0.024 mole of C₆H₈O₇—H₂O(citric acid) were mixed and stirred in 20 ml ofan ethanol solvent to prepare LaCoO₃ precursor sol. The laminationmembers A₉ and B₂ were impregnated with this precursor sol, and afterhaving been taken out, extra sol was removed by a suction process, andthe resulting matter was dried at 100° C., and fired at 600° C. for onehour so that a lamination member A₁₄ and a lamination member B₇ wereobtained. Here, the perovskite structure of LaCoO₃ was confirmed throughX-ray diffraction measurements. The amount of deposition of the catalystwas 30 g/l.

(2) Laminating Process

A casing (cylindrical metal container) having a pressing member on oneside was placed with the side to which the pressing member was attachedfacing down. After five of the lamination members B₇ had been laminated,140 of the lamination members A₁₄ were laminated, and five of thelamination members B₇ were lastly laminated thereon; moreover, this wasthen subjected to a pressing process, and a pressing member was alsoplaced on the other side so as to be secured so that a honeycombstructural body made of a laminated body having a length of 150 mm wasprepared.

Here, in this process, the respective lamination members were laminatedso that the through holes were superposed on one another.

Comparative Example 1

(1) Powder of α-type silicon carbide having an average particle size of10 μm (80% by weight) and powder of β-type silicon carbide having anaverage particle size of 0.5 μm (20% by weight) were wet-mixed, and to10 parts by weight of the resulting mixture were added and kneaded 5parts by weight of an organic binder (methyl cellulose) and 10 parts byweight of water to obtain a kneaded matter. Next, after a slight amountof a plasticizer and a lubricant had been further added and kneadedtherein, the resulting mixture was extrusion-molded so that a raw moldedproduct was formed.

Next, the above-mentioned raw molded product was dried by using amicro-wave drier, and after predetermined through holes had been filledwith a paste having the same composition as the raw molded product, theresulting product was again dried by using a drier. Thereafter, this wasthen degreased at 400° C., and fired at 2200° C. in a normal-pressureargon atmosphere for 3 hours to manufacture a porous ceramic member,which was a silicon carbide sintered body, and had a size of 33 mm×33mm×150 mm, the number of through holes of 3.1 pcs/cm² and a thickness ofthe through holes of 2 mm.

By using a heat resistant adhesive paste containing 19.6% by weight ofalumina fibers having a fiber length of 0.2 mm, 67.8% by weight ofsilicon carbide particles having an average particle size of 0.6 μm,10.1% by weight of silica sol and 2.5% by weight of carboxymethylcellulose, a large number of the porous ceramic members were combinedwith one another, and this was then cut by using a diamond cutter toform a cylindrical ceramic block having a diameter of 141.8 mm.

Next, ceramic fibers made from alumina silicate (shot content: 3%, fiberlength: 0.1 to 100 mm) (23.3% by weight), which served as inorganicfibers, silicon carbide powder having an average particle size of 0.3 μm(30.2% by weight), which served as inorganic particles, silica sol (SiO₂content in the sol: 30% by weight) (7% by weight), which served as aninorganic binder, carboxymethyl cellulose (0.5% by weight), which servedas an organic binder, and water (39% by weight) were mixed and kneadedto prepare a sealing material paste.

Next, a sealing material paste layer having a thickness of 1.0 mm wasformed on the circumferential portion of the ceramic block by using theabove-mentioned sealing material paste. Further, this sealing materialpaste layer was dried at 120° C. so that a cylindrical honeycombstructural body was manufactured. Then, Pt was adhered to this honeycombstructural body at a rate of 5 g/l by using a conventional method (inwhich the honeycomb structural body was immersed in alumina slurrybearing Pt).

Next, a casing (cylindrical metal container) having a pressing member onone side was placed with the side to which the pressing member wasattached facing down. After the honeycomb structural body bearing theplatinum catalyst deposited thereon had been assembled in the casingwith a holding sealant member wound thereon, another pressing member wasalso put on the other side so as to be secured so that an exhaust gaspurifying device in which the honeycomb structural body having a lengthof 150 mm was assembled into a casing was prepared.

Comparative Example 2

As shown in FIG. 7(a) a three-dimensional mesh-shape porous member, madeof Ni—Cr alloy (trade name: CELMET, average pore diameter: 400 μm, madeby Sumitomo Electric Industries Ltd.), was compressed by a roller so asto have an average pore diameter of 80 μm, and formed into a sheethaving a thickness of 2 mm; and then, tubular filters 81 and 82, formedby winding these sheets eight times, are combined with each other in aconcentric manner, and iron plates 84 are attached to two end faces withgaskets interposed therebetween in staggered fashion on the gas inletside and the gas outlet side so that a filter element 80 wasmanufactured. By assembling seven sets of these filter elements 80 in acasing (a cylindrical metal container) with equal intervals so that anexhaust gas purifying device was formed. Here, FIG. 7(b) is across-sectional view that schematically shows a cross section inparallel with the length direction of the filter element 80 shown inFIG. 7(a). As indicated by arrows shown in FIG. 7(b), gases are directedbetween the tubular filters 81 and 82, and allowed to pass through therespective filters and flow outside of the tubular filter 81 or insideof the tubular filter 82.

Comparative Example 3

First, two sheets of belt-shaped flat-plate stainless foil 97 andcorrugated stainless foil 98 are wound to form multiple layers in whichthese foils are located alternately, and the contact portions of theflat-plate stainless foil 97 and the corrugated stainless foil 98 arebrazed to each other so that a honeycomb structural body 90 having aroll shape as a whole, as shown in FIG. 8, was formed (corrugatingprocess). Further, a catalyst substance, prepared by mixing poroussilica powder, inorganic fibers (reinforcing material), inorganicbinding agent, water and organic binding agent, was applied to the outersurface of a cell wall 91 forming the honeycomb structural body 90. Thecatalyst substance was left at normal temperature, and almost dried, andthis was then heated at 500 to 600° C. for 40 minutes so that ahoneycomb structural body 90 bearing the catalyst deposited therein wasmanufactured. In this honeycomb structural body 90, exhaust gases areallowed to pass through a number of hollow columnar cells 92 that areformed as separated sections by the cell walls 91.

Next, a casing (cylindrical metal container) having a pressing member onone side was placed with the side to which the pressing member wasattached facing down. After the honeycomb structural body bearing thecatalyst deposited therein had been assembled in a casing, anotherpressing member was also put on the other side so as to be secured sothat an exhaust gas purifying device in which the honeycomb structuralbody having a length of 150 mm was assembled into a casing was prepared.

(Evaluation Method)

(1) Occurrence of Damages Due to Regenerating Process

The same exhaust gas purifying devices as those of the examples andcomparative examples were manufactured except that no catalyst wasdeposited thereon, and each of these was placed in an exhaust passage ofan engine. Then, the engine was driven at the number of revolutions of3000 min⁻¹ and a torque of 50 Nm until 1 g of particulates per 100 g ofthe filter had been collected, and the filter was then subjected to aregenerating process to burn the particulates. Here, with respect to thehoneycomb structural bodies of Examples 1 to 14, upon regenerating,temperatures inside the filter were measured at the lamination memberslocated before and after a portion 20 mm apart from the exhaust gasinlet side as well as at the lamination members located before and aftera portion 20 mm apart from the exhaust gas outlet side. Further, at eachof the portions, a temperature difference occurring in the lengthdirection per one sheet of the lamination layers was measured. Moreover,with respect to the honeycomb structural bodies or filter elements ofComparative Examples 1 to 3, temperatures were measured at a portion 20mm apart from the exhaust gas inlet side as well as at a portion 20 mmapart from the exhaust gas outlet side. Then, a temperature differenceoccurring in the length direction of the honeycomb filter or the filterelement was measured. Table 1 shows the results of the measurements.

Further, the above-mentioned particulate collecting process andregenerating process are respectively repeated 100 times, and each ofthe honeycomb structural bodies or the filter elements was cut along aface perpendicular to the length direction thereof, and the cut face wasvisually observed for occurrence of any damages. Table 1 shows theresults.

(2) Changes in Pressure Loss upon Collection of Particulates

Each of the exhaust gas purifying devices according to the examples andcomparative examples was placed in an exhaust passage of an engine, andthe engine was driven at the number of revolutions of 1200 min⁻¹ and atorque of 10 Nm for 100 minutes so that the initial pressure loss beforecollecting particulates and the pressure loss after collection of 3 g/lof particulates were measured. Table 2 shows the results.

(3) Porosity of Honeycomb Structural Body or Filter Element

With respect to each of the honeycomb structural bodies or filtersaccording to the respective examples and comparative examples, theporosity was measured by a weight porosity measuring method. Table 2shows the results.

(4) Change in Collecting Efficiency upon Regenerating

Each of the exhaust gas purifying devices according to the respectiveexamples and comparative examples was placed in an exhaust passage of anengine, the engine was driven at the number of revolutions of 3000 min⁻¹and a torque of 50 Nm until 1 g of particulates per 100 g of the exhaustgas purifying device or the filter had been collected; thereafter, thiswas then subjected to a regenerating process to burn the particulates.These processes were defined as one cycle, and 51 cycles of theparticulate-collecting and regenerating processes were repeated. Duringthe tests, the amount of particulates collected by the honeycombstructural body or the filter element and the amount of particulatesthat were not collected were respectively measured; thus, the collectingefficiencies of particulates were confirmed respectively, at the initialstate before collection of particulates, after one time of theregenerating process and after 50 times of the regenerating processes.Table 2 shows the results.

Here, the collecting efficiency of particulates refers to a ratio ofparticulates collected by the honeycomb structural body or the filterelement to the particulates in exhaust gases that were allowed to flowinto the exhaust gas purifying device. TABLE 1 Temperature differenceThickness upon regenerating (° C.) of Lamination Lamination Presence orConstituent Weight lamination member on member on absence of material(g) Structure member (mm) inlet side outlet side damage Example 1 Metal800 Lamination type 1 0 1 Absence Example 2 Metal 800 Lamination type 21 1 Absence Example 3 Metal 800 Lamination type 4 1 2 Absence Example 4Metal 800 Lamination type 1 0 1 Absence Example 5 Metal + 500 Laminationtype 1 1 2 Absence Inorganic fiber Example 6 Metal + 500 Lamination type5 2 5 Absence Inorganic fiber Example 7 Metal + 500 Lamination type 1015 25 Absence Inorganic fiber Example 8 Metal + 500 Lamination type 1 12 Absence Inorganic fiber Example 9 Metal fiber 800 Lamination type 1 01 Absence Example 10 Metal fiber + 500 Lamination type 1 1 2 AbsenceInorganic fiber Example 11 Inorganic fiber 500 Lamination type 1 1 2Absence Example 12 Inorganic fiber 500 Lamination type 1 1 2 AbsenceExample 13 Metal 500 Lamination type 1 1 2 Absence Example 14 Metalfiber 500 Lamination type 1 1 2 Absence Comparative Refractory 1150Integral type — 170 Presence Example 1 particle Comparative Metal 880Element type — 80 Absence Example 2 Comparative Metal 800 Corrugate type— 85 Absence Example 3

TABLE 2 Pressure loss (kPa) Collecting efficiency (%) After After AfterInitial collection Porosity Initial regenerating regenerating state of 3g/l (% by volume) state process of one time process of 50 times Example1 10.5 15.9 90 80 80 80 Example 2 10.7 15.1 90 80 80 80 Example 3 10.915.5 90 80 80 80 Example 4 12.4 14.2 90 85 85 85 Example 5 10.3 15.7 9080 75 65 Example 6 10.6 15.2 90 80 80 70 Example 7 10.9 15.9 90 80 80 70Example 8 12.6 14.8 90 85 80 70 Example 9 11.4 16.1 85 80 80 80 Example10 10.9 15.8 90 80 75 65 Example 11 10.3 14.5 90 80 75 60 Example 12 9.513.5 90 80 75 60 Example 13 9.7 14.8 90 80 80 80 Example 14 10.1 15.0 8580 80 80 Comparative 14.6 32.8 70 90 90 0 Example 1 Comparative 23.536.7 90 70 70 70 Example 2 Comparative 18.5 31.1 90 75 75 75 Example 3

As clearly indicated by the results shown in Table 1, with respect tothe honeycomb structural bodies according to Examples 1 to 14, atemperature difference occurring per one lamination member uponregenerating was in a range from 0 to 25° C.

In contrast, with respect to the honeycomb structural body according toComparative Example 1, a temperature difference occurring in thehoneycomb structural body upon regenerating was 170° C.

For this reason, as shown in Table 1, with respect to the honeycombstructural body according to Comparative Example 1, damages wereobserved after a regenerating process; in contrast, with respect to thehoneycomb structural bodies according to Examples 1 to 14, no damage wasobserved after a regenerating process.

As clearly indicated by the results shown in Table 2, with respect tothe honeycomb structural bodies according to Examples 1 to 14, theporosity was increased in comparison with the honeycomb structural body(Comparative Example 1) formed by firing ceramic particles so that itwas possible to reduce the initial pressure loss and the pressure lossupon collecting particulates. In contrast, with respect to the filterelement according to Comparative Example 2 and the honeycomb structuralbody according to Comparative Example 3, although the porosity wasincreased, the initial pressure loss and the pressure loss uponcollecting particulates were low due to the structures thereof.

Moreover, with respect to the honeycomb structural bodies according toExamples 1 to 10, 13 and 14, since metal was used as a constituentmaterial, the collecting efficiency was high even after repetitiveregenerating processes. This is because, since the metal has a very highcoefficient of thermal expansion in comparison with ceramics, the metalwas expanded in the length direction as well as in the diameterdirection in the honeycomb structural body at high temperatures (duringuse) so as to fill fine gaps between the lamination members and gaps tothe casing.

Furthermore, with respect to the honeycomb structural bodies accordingto Examples 4 and 8, since irregularities were formed on the innersurface of each bottomed hole in the wall portion, the initialcollecting efficiency was improved in these honeycomb structural bodies.

In contrast, with respect to the filter element according to ComparativeExample 2 and the honeycomb structural body according to ComparativeExample 3, the initial collecting efficiency was low due to thestructures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a perspective view that schematically shows one example ofa honeycomb structural body in accordance with the invention; and FIG.1(b) is a cross-sectional view taken along line A-A of the honeycombstructural body shown in FIG. 1(a).

FIG. 2(a) is a perspective view that schematically shows laminationmembers that constitute the honeycomb structural body of the presentinvention; and FIG. 2(b) is a perspective view that shows amanufacturing process in which the honeycomb structural body of thepresent invention is formed by laminating the lamination members shownin FIG. 2(a).

FIG. 3 is a cross-sectional view that schematically shows one example ofan exhaust gas purifying device using the honeycomb structural body ofthe present invention.

FIG. 4 is a perspective view that schematically shows a conventionalfilter that has a honeycomb structure.

FIG. 5(a) is a perspective view that schematically shows a porousceramic member that forms the filter having a honeycomb structure shownin FIG. 4; and FIG. 5(b) is a cross-sectional view taken along line B-Bof the porous ceramic member shown in FIG. 5(a).

FIG. 6(a) is a perspective view that schematically shows another exampleof the honeycomb structural body of the present invention, and FIG. 6(b)is a perspective view that schematically shows still another example ofthe honeycomb structural body of the present invention.

FIG. 7(a) is an enlarged cross-sectional view that schematically shows awall portion interposed between through holes in the honeycombstructural body of the present invention, and FIG. 7(b) is across-sectional view that schematically shows a wall portion interposedbetween through holes in a honeycomb structural body made from ceramics,which continuously extend in the length direction.

FIG. 8 is a perspective view that schematically shows a honeycombstructural body according to Comparative Example 3.

FIG. 9(a) is a cross-sectional view that schematically shows a wallportion interposed between through holes in a honeycomb structural bodyof the present invention, and FIG. 9(b) is a cross-sectional view thatschematically shows a wall portion interposed between through holes in anormal honeycomb structural body made from ceramics, which has anintegral structure.

EXPLANATION OF SYMBOLS

-   10, 20, 30, 40 honeycomb structural body-   10 a, 10 b, 30 a, 40 a lamination member-   11 bottomed hole (through hole)-   13 wall portion-   23 casing-   200 exhaust gas purifying device

1. A pillar-shaped honeycomb structural body having a structure in whicha plurality of through holes are placed in parallel with one another inthe length direction with a partition wall interposed therebetween,wherein lamination members are laminated in the length direction so thatthe through holes are superposed on one another, and one of ends of eachthrough hole is sealed.
 2. A pillar-shaped honeycomb structural bodyhaving a structure in which a plurality of through holes are placed inparallel with one another in the length direction with a partition wallinterposed therebetween, wherein lamination members are laminated in thelength direction so that the through holes are superposed on oneanother, and at least the lamination members positioned on both endfaces of the honeycomb structural body are mainly made of metal.
 3. Thehoneycomb structural body according to claim 2, wherein all thelamination members are mainly made of metal.
 4. The honeycomb structuralbody according to claim 2 or 3, wherein each of a plurality of thethrough holes is sealed at one of the ends of the honeycomb structuralbody, and the honeycomb structural body functions as a filter.
 5. Thehoneycomb structural body according to claim 1 or 2, wherein a catalystis supported on the lamination members.
 6. The honeycomb structural bodyaccording to claim 1 or 2, which functions as a filter for an exhaustgas purifying device.
 7. A pillar-shaped honeycomb structural bodyhaving a structure in which a plurality of through holes are placed inparallel with one another in the length direction with a partition wallinterposed therebetween, wherein lamination members having differentshapes or sizes of the through holes are laminated in the lengthdirection so that the through holes are superposed on one another and asurface of the partition wall has an irregularity, and one of ends ofeach through hole is sealed.
 8. A pillar-shaped honeycomb structuralbody having a structure in which a plurality of through holes are placedin parallel with one another in the length direction with a partitionwall interposed therebetween, wherein lamination members havingdifferent shapes or sizes of the through holes are laminated in thelength direction so that the through holes are superposed on one anotherand a surface of the partition wall has an irregularity, and at leastthe lamination members positioned on both end faces of the honeycombstructural body are mainly made of metal.